Liquid feed pump apparatus

ABSTRACT

An adjustment channel is connected to first and second pump mechanisms in parallel therewith. The flow of a liquid sent by pump heads is split, and part of the liquid is sent to an outlet port side, while the remaining liquid flows through the adjustment channel and is returned to an inlet port side. The adjustment channel has a restrictor which is so arranged that the flow rate is set to 100 μL/min to 1 mL/min, and pressure of 2 MPa to 20 MPa or thereabouts is applied thereto. In micro LC and nano LC, the flow rate of a column is 100 nL/min to 10 μL/min or thereabouts, and pressure of several MPa to 20 MPa or thereabouts is applied. Therefore, of the liquid sent from the pump mechanism, 0.1% to 1% is delivered from the outlet port, while the remaining liquid flows through the adjustment channel and is returned to the inlet port side.

Th is application claims foreign priority based on Japanese patent application JP 2003-382678, filed on Nov. 12, 2003, the contents of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid feed pump apparatus for feeding a liquid, such as feeding an eluent for a liquid chromatograph.

2. Description of the Related Art

In the related art, as pumps for micro high performance liquid chromatography (micro LC) and nano high performance liquid chromatography (nano LC), the following two systems are known: a system in which the flow of the mobile phase at a flow rate of 100 to 1000 μL/min is split by using a splitter to feed the liquid only at a required flow rate (splitter system); and a system in which a very small quantity is directly sucked and fed (direct system).

With the liquid feed pump of the splitter system, since the resistance of the splitter changes with the lapse of time, it is difficult to stabilize the flow rate over a long period of time. In addition, there is a problem in that since the split mobile phase other than the liquid at a necessary flow rate is discharged, the mobile phase is consumed wastefully.

With the liquid feed pump of the direct system, in a case where the feeding rate is very low, the flow rate is greatly affected even by a slight fluctuation of the pump operation. Hence, there is a problem in that pulsation and irregularities in liquid feeding are likely to occur.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a liquid feed pump apparatus which is capable of feeding the liquid stably even at a very low feeding rate by correcting wasteful consumption of the mobile phase and pulsation and irregularities in liquid feeding due to the pump operation, which have been the related-art problems.

In accordance with the invention there is provided a liquid feed pump apparatus comprising: a pump head for sucking a liquid from an inlet port and feeding the liquid from an outlet port; a flow meter provided on an outlet port side of the pump head to measure a flow rate of the liquid fed to an outside from the outlet port; an adjustment channel provided in parallel with the pump head to return to an inlet port side of the pump head part of the liquid which is sent to the outlet port of the pump head; and a controller to which an output of the flow meter is inputted and which controls the driving of the pump so that a value of the output of the flow meter becomes a predetermined value.

By virtue of this configuration, part of the fed liquid from the outlet port side of the pump head is returned to the inlet port side through the adjustment channel, and the flow rate is measured on the outlet port side to feed back an error with respect to a set value, thereby controlling the operational speed of the pump.

The greater the rate at which the liquid is returned from the outlet port side to the inlet port side through the adjustment channel, the more suitable it is for feeding at a very low rate.

In addition, an opening valve may be provided in the adjustment channel.

Since part of the liquid to be fed from the outlet port is returned to the inlet port side through the adjustment channel, it becomes possible for the pump head to feed at a greater rate than at the flow rate for feeding the liquid from the outlet port to the outside. Therefore, it becomes possible to shorten the operating cycle of the pump, thereby making it possible to reduce the effects of pulsation and irregularities in liquid feeding. In addition, since the feeding rate is measured by providing the flow meter on the outlet port side, and an error between its measured value and a set value is fed back, it becomes possible to stabilize the feeding rate.

If the opening valve is provided in the adjustment channel, it becomes possible to change over the on/off operation of the liquid flow into the adjustment channel and cope with the feeding rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow channel diagram illustrating an exemplary, non-limiting basic configuration of an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, a description will be given of one embodiment.

FIG. 1 is a flow channel diagram illustrating an exemplary, non-limiting basic configuration of an embodiment in which the invention is applied to a double plunger type pump.

A liquid feed pump apparatus in accordance with this embodiment is comprised of two pump mechanisms. A pump head 7 of the first pump mechanism consists of a plunger 4 a, an inlet side check valve 8, and an outlet side check valve 6. In this pump head 7, as the plunger 4 a moves to the right in the drawing (retracts), the check valve 8 is opened, and the check valve 6 is closed. This allows a fluid to be sucked through an inlet port 14 and to be accumulated in a space 7 a formed in the pump head 7. When the plunger 4 a moves to the left in the drawing (advances), this time the check valve 6 is opened, and the check valve 8 is closed, so that the liquid accumulated in the space 7 a is pushed out by the plunger 4 a.

A pump head 11 of the second pump mechanism similarly consists of a plunger 4 b, an inlet side check valve 12, and an outlet side check valve 10. In this pump head 11 as well, as the plunger 4 b moves to the right in the drawing, the check valve 12 is opened, and the check valve 10 is closed. This allows the fluid to be sucked through the inlet port 14 and to be accumulated in a space 11 a formed in the pump head 11. When the plunger 4 b moves to the left in the drawing, this time the check valve 10 is opened, and the check valve 12 is closed, so that the liquid accumulated in the space 11 a is pushed out by the plunger 4 b.

The plunger 4 a is adapted to be constantly brought into contact with an outer peripheral surface of a cam 2 a, and as the cam 2 a rotates, the plunger 4 a under goes reciprocating motion. Similarly, the plunger 4 b is adapted to be constantly brought into contact with an outer peripheral surface of a cam 2 b, and as the cam 2 b rotates, the plunger 4 b undergoes reciprocating motion. The cams 2 a and 2 b are connected to a common motor 2 serving as a driving mechanism. The cam 2 a and the cam 2 b are connected to the motor 2 so that the sucking and delivery operations of the plunger 4 a and the plunger 4 b are effected alternatively, so as to allow continuous feeding of the liquid.

In this liquid feed pump apparatus, an adjustment channel 40, which is connected between the inlet port sides and the outlet port sides of the respective pump heads 7 and 11, is provided in parallel for the first and second pump mechanisms. The flow of the liquid sent by the pump heads 7 and 11 is split by this adjustment channel 40, and part of the liquid is sent to an outlet port 15 side, while the remaining liquid flows through the adjustment channel 40 and is returned to the inlet port side. The adjustment channel 40 is provided with a restrictor 16, and this restrictor 16 is so arranged that the flow rate is set to 100 μL/min to 1 mL/min, and pressure of 2 MPa to 20 MPa or thereabouts is applied thereto. In micro LC and nano LC, the flow rate of a column is 100 nL/min to 10 μL/min or thereabouts, and pressure of several MPa to 20 MPa or thereabouts is applied. Therefore, of the liquid sent from the pump heads 7 and 11, 0.1% to 1% is delivered from the outlet port 15, while the remaining liquid flows through the adjustment channel 40 and is returned to the inlet port side.

A top valve (opening valve) 18 is provided upstream of the restrictor 16 of the restrictor channel 40. The arrangement provided is such that as this valve 18 is opened or closed, whether or not the liquid is allowed to flow across the restrictor 16 can be changed over.

Reference numerals 32 and 34 denote channels through which the liquid passes when it is sucked from the inlet port 14 into the pump heads 7 and 11. Reference numeral 36 denotes a channel through which part of the liquid sent from the pump heads 7 and 11 is sent to the outlet port 15. The part of the liquid sent from the pump head 11 flows cross a channel 38, subsequently flows through the channel 36, and is sent to the outlet port 15. Further, when the liquid is sent from the pump head 7, part of the liquid sent passes through the channel 38 and flows into the adjustment channel 40.

A flow meter 22 is provided upstream of the outlet port 15 and downstream of a branch point for the adjustment channel, so as to measure the rate of flow of the liquid sent from the first and second pump mechanisms to the outlet port 15.

In addition, a controller 24 is connected to the flow meter 22. A value of the flow rate outputted from the flow meter 22 is inputted to the controller 24, and the controller 24 compares it with a preset flow rate and controls the motor 2 so as to reduce its error. Thus, the quantity of the liquid fed is constantly measured by the flow meter 22, a comparison is made with a predetermined flow rate, and the number of revolutions of the motor 2 is controlled in correspondence with the result. Therefore, it is possible to attain the stabilization of the quantity of the fluid sent to the outlet port 15.

Hereafter, a description will be given of the operation of the liquid feed pump apparatus of this embodiment along with the flow of the liquid.

As the motor 2 rotates, the cams 2 a and 2 b attached to the motor 2 rotate to reciprocate the plungers 4 a and 4 b. In the first pump mechanism located above in FIG. 1, as for the check valves 6 and 8, when the plunger 4 a moves to the right, the check valve 6 is closed, and the check valve 8 is opened, whereas when the plunger 4 a moves to the left, the check valve 8 is closed, and the check valve 6 is opened. When the plunger 4 a moves to the right, the space 7 a is formed in the pump head 7, and the liquid is sucked into it from the inlet port 14 through the channel 32. When the plunger 4 a moves to the left, the liquid sucked into the space 7 a is pushed out and is sent through the check valve 6 by the pump head 7. The flow of the liquid fed by the pump head 7 is split into the liquid which flows through the channel 36 and is sent to the outlet port 15 and the liquid which flows through the channel 38 and the adjustment channel 40 and is returned to the inlet port side.

In the second pump mechanism located below, as for the check valves 10 and 12, when the plunger 4 b moves to the right, the check valve 10 is closed, and the check valve 12 is opened, whereas when the plunger 4 b moves to the left, the check valve 12 is closed, and the check valve 10 is opened. When the plunger 4 b moves to the right, the space 11 a is formed in the pump head 11, and the liquid is sucked into it from the inlet port 14 through the channel 34. When the plunger 4 b moves to the left, the liquid sucked into the space 11 a is pushed out, and is sent through the check valve 10 by the pump head 11. The flow of the liquid fed by the pump head 11 is split into the liquid which flows through the channels 38 and 36 and is sent to the outlet port 15 and the liquid which flows through the adjustment channel 40 and is returned to the inlet port side.

The flow rate of the liquid which is fed from the first or second pump mechanism and flows through the channel 36 is measured by the flow meter 22. The result of measurement of the flow rate measured by the flow meter 22 is inputted to the controller 24. A desired flow rate is set in advance in the controller 24, and the rotational speed of the motor 2 is controlled such that the result of measurement from the flow meter 22 conforms to the set flow rate.

In a state in which the stop valve 18 is open, major portions of the liquid sent from the pump heads 7 and 11 flow through the adjustment channel 40 and are returned to the inlet port. Since the liquid which is not delivered from the outlet port 15 is returned to the inlet port, it is possible to increase the quantity of the liquid sent from the pump heads 7 and 11 relative to the quantity of the liquid delivered from the outlet port 15, so that it is possible to prevent irregularities in liquid feeding and pulsation. In addition, since the period of operation of the pump is shortened, effects of pulsating flow and variations in concentration become small.

With related-art pumps, in a case where the liquid is fed at a rate of 1 μL/min, if it is assumed that the stroke capacity of the plunger is 10 μL, since the plunger reciprocates in every 10 minutes, irregularities occurred in liquid feeding at a cycle of 10 minutes. In the invention, however, the rate of the liquid fed from the plunger can be 100 μL/min or thereabouts, so that the irregularities in liquid feeding due to the reciprocating cycle of the plunger practically do not affect the analysis.

Preferably, the valve 18 should be kept open in a case where the feeding flow rate is a micro flow rate or a nano flow rate, and the valve 18 should be kept closed in a case where the feeding flow rate is a semi-micro flow rate or more (approx. 100 μL/min or more)

The configuration of the invention is similarly applicable also to a pump having one plunger and one pump head.

The downstream end of the adjustment channel may not be connected to the intake channels 32 and 34, and may be connected to a mobile phase tank or the like so as to be returned. In that case as well, since it is possible to increase the quantity of the liquid sent from the pump heads 7 and 11 relative to the quantity of the liquid delivered from the outlet port 15, it is possible to prevent irregularities in liquid feeding and pulsation.

An arrangement may be provided such that the opening and closing of the stop valve 18 is controlled in correspondence with a feeding rate by the controller 24.

In addition, an arrangement may be provided such that the channel resistance of the adjustment channel 40 is adjusted by the use of a valve or the like.

It will be apparent to those skilled in the art that various modifications and variations can be made to the described preferred embodiment of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover all modifications and variations of this invention consistent with the scope of the appended claims and their equivalents. 

1. A liquid feed pump apparatus comprising: a pump head for sucking a liquid from an inlet port and feeding the liquid from an outlet port; a flow meter provided on an outlet port side of the pump head to measure a flow rate of the liquid fed to an outside from the outlet port; an adjustment channel provided in parallel with the pump head to return to an inlet port side of the pump head part of the liquid which is sent to the outlet port of the pump head; and a controller to which an output of the flow meter is inputted and which controls the driving of the pump head so that a value of the output of the flow meter becomes a predetermined value.
 2. The liquid feed pump according to claim 1, further comprising: an opening valve provided in the adjustment channel.
 3. The liquid feed pump according to claim 1, further comprising: a restrictor provided in the adjustment channel, in which the flow rate is set to 100 μL/min to 1 mL/min, and pressure of 2 MPa to 20 MPa or thereabouts is applied thereto. 